Electron-discharge device with indirectily-heated cathode



June 24, 1930. c. E. HUFFMAN ELECTRON DISCHARGE DEVICE WITH INDIRECTLY HEATED GATHODE Filed July 1, 1927 Patented June 24, 1930 UNITED STATES PATENT OFFICE CHARLES E. HUFFMAN, OF MONTGLAIR, NEW JERSEY, ASSIGNOR TO WESTINGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA ELECTRON-DISCHARGE DEVICE WITH INDIRECTLY-HEATED CATI-IODE Application filed. July 1, 1927. Serial No. 202,812.

This invention relates to an electron discharge device and more particularly to such a device having an anode, cathode and one or more grid electrodes in which alternating current is employed for heating the cathode to an electron emitting temperature.

The invention is especially concerned with electron discharge devices designed for use in radio receiving apparatus and having the cathode heated by radiation or conduction from a heater element, electrically insulated therefrom and energized by alternating current of suitable voltage, although it is applicable to other types of devices in which the cathode is heated by the direct passage of alternating current therethrough.

Heretofore, in the construction of indirectly heated cathode tubes, ditiiculty has been experienced due to the objectionable hum produced by the interfering action of the alternation of current in the leads supplying the heater element, upon the leads of the control electrode. To overcome this difficulty, it has been the practice to bring out the leads for the grid at the opposite end of the tube from the alternating current supply leads. In the usual construction, the grid, anode and cathode leads terminate in the usual base and the alternating current leads were brought out through the top of the tube to separate terminals. This construction is also objectionable in that it necessitates the draping of the alternating current supply conductors over the tops of the tubes in more or less close proximity to the induction coils, thus causing the alterations in current to be. induced therein. This construction is further objectionable in that it requires that the heater conductors be joined to and disconnected from the tube terminals whenever it is desired to remove or replace a tube.

One of the objects of the present invention is to overcome the above mentioned ditliculties and enable the alternating current heater leads to be brought out through the same end of the tube as the remaining leads.

A further object is to provide an arrangement of electrode leads in which the interfering influence of the alternating current leads on the grid lead is rendered negligible.

A further object is to provide an arrangement of terminal prongs in the base whereby the grid electrode terminal is protected from the influence of the alternating current supply terminals.

A still further object is to provide a terminal arrangement for an indirectly heated cathode radio tube which will facilitate replacement of the tube in receiving apparatus.

Another object is to provide an arrangement of terminal prongs in the tube base by which the magnetic fields set up by the heater terminals will be partially neutralized:

Other objects and advantages will hereinafter appear.

In accordance with my invention, I seal the leading-in wires for the heater element in the same press with the grid, anode and cathode leads and so shield the grid lead from the alternating current beater leads that they do not induce any objectional currents therein. I have found that when a conductor maintained at substantially ground potential is interposed in the press between the alternating current leads and the grid lead, that the bum which ordinarily results when the heater lea ds are brought out through the same end of the tube as the grid lead, is materially reduced. This shielding conductor may conveniently be the cathode lead, although a separate conductor may be employed if desired.

The electrode leads are all secured to ter minal prongs in a common base, the prongs of which are likewise arranged to prevent undesirable fields being set up about the grid terminal.

In order that the invention may be more fully understood. reference will be had to the accompanying drawing in which:

Fig. 1 is a sectional view of a vacuum tube constructed in accordance with my invention I Fig. 2 is a plan View of the base showingone arrangement of terminal prongs Fig. 3 is a plan view of the base showing a. different arrangement of terminal prongs; and,

Fig. 4 is a circuit diagram in which the tube of Figs. 1, 2 and 3 is employed.

Referring to Fig. 1, there is shown an envelope 5 having a neck 6 to which the usual stem 7 is sealed. A press 8 is formed at the upper end of the stem, through which the leading-in conductors are sealed and from which the electrode assembly 9 is supported. The electrode assembly comprises a cylindrical anode 11, grid or control electrode 12 disposed therein, and a cathode 13 concentric with the anode and grid. The cathode 13 comprises a metal sleeve 14 coated with an electron emittin material, such as alkaline earth oxide, and is supported on an insulating body 15 having a refractory, filamentary heating element 16 threaded through apertures 17 in the insulating support for heat ing the cathode to an electron emitting temerature. This specific construction is old 1n the art and forms no part of the present invention.

The alternating current leads 18 and 19 for the heater element 16 are sealed through the press somewhat centrally thereof and the anode lead 20 is sealed at one side thereof.

The grid lead 21 is arranged at the opposite side of the heater leads and the cathode lead 22 is interposed between the grid lead and the heater leads. Of course, it is to be understood that other arrangements of the leadingin conductors in the ress may be employed, the essential feature eing that the grid lead be shielded from the alternating current lead by an interposed conductor which is maintained at substantially ground potential. This interposed conductor serves to prevent the alterations in the cathode heating current from setting up undesirable currents in the grid lead which would be amplified in the plate circuit, I

The conducting leads 18, 19, 20, 21 and 22 are joined to the terminal prongs 23, 24, 25, 26 and 27 respectively which may be arranged in the manner illustrated in Figs. 2 or 3. In

- Fig. 2, the alternating current heater terminals 23 and 24 are disposed relatively close together so as' to partially neutralize the changing magnetic fields caused by the alternating current flow through the leadingin wires contained therein. The gridprong 26 and plate prong 25 are disposed a relative- 1y long distance from the heater prongs to reduce interfering influence of the heating current. Interposed between the heater prong and the grid and plate prongs is the spaced a uniform distance from each of the heater prongs 23' and 24' and consequently the magnetic fields set up by the two heater terminals in the region of the grid prong neutralize each other.

The cathode prong 27' and the anode prong 25 are arranged intermediate the heater prongs and serve to overcome the interfering influence of the heating current.

In Fig. 4, I have illustrated a conventional c1rcu1t employing an indirectly heated cathode tube. In this diagram the tube 5' is prov1ded with the cathode 13, heater element 16', grid 12' and anode 11'. The cathode 13 1s grounded through the conductors 28 and 29 and the grid and plate returns are connected to the cathode by conductors 30 and 31 respectively, through the conductor 28. The cathode heater element 16' is provided with alternating heating current by a suitable transformer 32 from the alternating current lines 33.

' It will be evident from the foregoing, that the cathode lead being grounded will serve as a shield to prevent the electro-static coupling between the leads of the heater element and the grid lead, both in the base and throughthe press.

The dotted lines 34 shown in Fig. 2 represent the static fields which would ordinarily exist if the cathode prong 27 was not interposed between the gr1d prong 26, plate prong 25 and the alternating current prongs 23 and 24. These fields are diverted away from the grid pron andto the cathode prong when the catho e prong is so interposed, as indicated by the dotted lines 35.

I have described and claimed in a copending application Serial No. 201,292 filed June 25, 1927, an adapter for enabling the indirectly heated cathode tube of the present invention to be applied directly in radio receiving apparatus designed for tubes having a directly heated cathode. This adapter when inserted in the socket of the receiving apparatus and alternating current heating leads joined thereto, serves as a socket for the present tube, enabling the same to be inserted in or removedfrom the apparatus without connecting or disconnecting any of the supply leads, thus rendering the tubes readily interchangeable and replaceable.

While I have described some particular embodiments of my invention, it is to be understood that the invention is susce tible to many changes and modifications wit out depositioned next to each other and the terminal for said control electrode being spaced at an equal distance from each of said terminals for said heating element.

In testimony whereof, I have hereunto subscribed my name this 30th day of June, 1927.

CHARLES E. HUFFMAN. 

